Optimising rotary nickel titanium file use in canal enlargement

on 21 August 2007

1. Carefully evaluate the tooth that will be treated, preferably with multiple radiograph views. Ideally these views are digital and as such can be manipulated with software. I use Dexis (Dexis digital radiography, Alpharetta, GA, USA) for its clarity, ease of use, reliability and integration capabilities. Pre-operative study of the canal anatomy before treatment can often tell the clinician what the expected final taper and tip size of the tooth may be.

2. Know your file system well. Practise in extracted teeth. Compare brands, not all RNT file systems are created equal – some may excel in the coronal third as orifice openers, others apically. Some might be very safe and resist fracture, other less resistant to fracture but cut very aggressively. Of the file systems I have tried, the very best blend of all characteristics has been the K3 RNT system (SybronEndo) for its flexibility, durability, cutting efficiency, fracture resistance, ease of use with regard to its packaging and pack configurations.

It is available in tip sizes that range from 15-60 and in tapers from .02, .04 and .06 as well as orifice openers of a fixed 25-tip size and various tapers, .08, .10 and .12. Across the widest range of canal anatomy, it is application. The same cannot be said of all other brands on the market.

3. Use hand files to negotiate canals first to make certain that they are open, patent and can be traversed along their entire length before using RNT files.

Except in the coronal third of wide-open roots, hand files are almost always placed into canals before their RNT counterparts. Instrumentation should generally involve a pattern of hand file negotiation or assurance of patency and glide path creation, RNT insertion, irrigation and insertion of the hand file again to assure patency and the sequence repeated.

4. Insertion of the RNT is gentle, passive, slow and deliberate. Many endodontists do not rely upon motors to reverse the file if an excessive torque load is placed on the instrument.

Engagement of the file is minimised on the canal walls ideally to 1-2 mm of dentine at a time and no more than 4-6 mm. Minimising the engagement of the file at all times will

significantly reduce the chance of fracture of the file due excessive torque. Do not leave the file rotating in the canal in a stationary position.

It should be in motion either apically or brought out of the canal. The above notwithstanding, the file is not pumped up and down in the canal. Pumping a RNT file risks that the file might be accidentally inserted into a previously undiscovered canal or anatomical entity that locks the files tip. Such locking of the tip can lead to tip fracture very quickly and without warning.

5. I use both the TCM III electric motor from SybronEndo and the Electrotorque TLC (KaVo). The Electrotorque TLC combines all electric handpiece functions (high, low and endodontic) into one box, which is attached onto the dental unit. The Electrotorque TLC has fibre optics and with the right burs and technique, amongst other capabilities, makes access through porcelain crowns predictable without fracture.

I run both of these electric motors in K3 RNT file use at 900 RPM with the torque control off. Clinicians are advised to work up to this speed if desired and not use this speed if they are new to RNT file enlargement of canal spaces.

6. Finally, irrigation and recapitulation are copious so that debris does not accumulate in the canal. Clinical debris is floated out of the canal passively during irrigation and taking a small hand file to the estimated or true working length after every RNT insertion ensures the patency of the canal space.

In addition, ultrasonic activation of irrigants is optimal. As possible, this technology should be brought into the clinical case, ideally, under the rubber dam and SOM. Using a viscous EDTA gel like FileEze (Ultradent, available through Optident in the UK) during early enlargement of a vital tooth can help hold the pulp in suspension and minimise the chances that pulp will be propelled apically into the narrowing cross sectional diameters of the canal space. I welcome your feedback.